diff --git a/RELEASE_NOTES.rst b/RELEASE_NOTES.rst
index 56cba97ab..647930883 100644
--- a/RELEASE_NOTES.rst
+++ b/RELEASE_NOTES.rst
@@ -29,6 +29,8 @@ ARTIQ-5
 * ``aqctl_corelog`` now filters log messages below the ``WARNING`` level by default.
   This behavior can be changed using the ``-v`` and ``-q`` options like the other
   programs.
+* On Kasli the firmware now starts with a unique default MAC address
+  from EEPROM if `mac` is absent from the flash config.
 
 
 ARTIQ-4
diff --git a/artiq/firmware/libboard_artiq/i2c_eeprom.rs b/artiq/firmware/libboard_artiq/i2c_eeprom.rs
new file mode 100644
index 000000000..fb89bd4a2
--- /dev/null
+++ b/artiq/firmware/libboard_artiq/i2c_eeprom.rs
@@ -0,0 +1,65 @@
+use i2c;
+use pca9548;
+
+#[cfg(soc_platform = "kasli")]
+const I2C_SWITCH0: u8 = 0x70;
+#[cfg(soc_platform = "kasli")]
+const I2C_SWITCH1: u8 = 0x71;
+
+/// [Hardware manual](http://ww1.microchip.com/downloads/en/DeviceDoc/24AA02E48-24AA025E48-24AA02E64-24AA025E64-Data-Sheet-20002124H.pdf)
+pub struct EEPROM {
+    busno: u8,
+    port: u8,
+    address: u8,
+}
+
+impl EEPROM {
+    pub fn kasli_eeprom() -> Self {
+        EEPROM {
+            busno: 0,
+            /// Same port as Si5324
+            port: 11,
+            address: 0xa0,
+        }
+    }
+
+    fn select(&self) -> Result<(), &'static str> {
+        let mask: u16 = 1 << self.port;
+        pca9548::select(self.busno, I2C_SWITCH0, mask as u8)?;
+        pca9548::select(self.busno, I2C_SWITCH1, (mask >> 8) as u8)
+    }
+
+    pub fn read<'a>(&self, addr: u8, buf: &'a mut [u8]) -> Result<(), &'static str> {
+        self.select()?;
+
+        Ok(()).and_then(|()| {
+            i2c::start(self.busno)?;
+            i2c::write(self.busno, self.address)?;
+            i2c::write(self.busno, addr)?;
+            Ok(())
+        }).map_err(|()| "I2C address write error")?;
+
+        Ok(()).and_then(|()| {
+            i2c::restart(self.busno)?;
+            i2c::write(self.busno, self.address | 1)?;
+            let buf_len = buf.len();
+            for (i, byte) in buf.iter_mut().enumerate() {
+                *byte = i2c::read(self.busno, i < buf_len - 1)?;
+            }
+
+            i2c::stop(self.busno)?;
+            Ok(())
+        }).map_err(|()| "I2C read error")?;
+
+        Ok(())
+    }
+
+    /// > The 24AA02XEXX is programmed at the factory with a
+    /// > globally unique node address stored in the upper half
+    /// > of the array and permanently write-protected.
+    pub fn read_eui48<'a>(&self) -> Result<[u8; 6], &'static str> {
+        let mut buffer = [0u8; 6];
+        self.read(0xFA, &mut buffer)?;
+        Ok(buffer)
+    }
+}
diff --git a/artiq/firmware/libboard_artiq/lib.rs b/artiq/firmware/libboard_artiq/lib.rs
index 1900719ec..300eed3a6 100644
--- a/artiq/firmware/libboard_artiq/lib.rs
+++ b/artiq/firmware/libboard_artiq/lib.rs
@@ -32,6 +32,8 @@ pub mod rpc_queue;
 mod pca9548;
 #[cfg(has_si5324)]
 pub mod si5324;
+#[cfg(soc_platform = "kasli")]
+pub mod i2c_eeprom;
 
 #[cfg(has_slave_fpga_cfg)]
 pub mod slave_fpga;
diff --git a/artiq/firmware/runtime/main.rs b/artiq/firmware/runtime/main.rs
index 97b6b88e2..5a96c3336 100644
--- a/artiq/firmware/runtime/main.rs
+++ b/artiq/firmware/runtime/main.rs
@@ -135,21 +135,36 @@ fn startup() {
         _ => {
             #[cfg(soc_platform = "kasli")]
             {
-                hardware_addr = EthernetAddress([0x02, 0x00, 0x00, 0x00, 0x00, 0x21]);
+                let eeprom = board_artiq::i2c_eeprom::EEPROM::kasli_eeprom();
+                hardware_addr =
+                    eeprom.read_eui48()
+                    .map(|addr_buf| {
+                        let hardware_addr = EthernetAddress(addr_buf);
+                        info!("using MAC address {} from EEPROM", hardware_addr);
+                        hardware_addr
+                    })
+                    .unwrap_or_else(|e| {
+                        error!("failed to read MAC address from EEPROM: {}", e);
+                        let hardware_addr = EthernetAddress([0x02, 0x00, 0x00, 0x00, 0x00, 0x21]);
+                        warn!("using default MAC address {}; consider changing it", hardware_addr);
+                        hardware_addr
+                    });
             }
             #[cfg(soc_platform = "sayma_amc")]
             {
                 hardware_addr = EthernetAddress([0x02, 0x00, 0x00, 0x00, 0x00, 0x11]);
+                warn!("using default MAC address {}; consider changing it", hardware_addr);
             }
             #[cfg(soc_platform = "metlino")]
             {
                 hardware_addr = EthernetAddress([0x02, 0x00, 0x00, 0x00, 0x00, 0x19]);
+                warn!("using default MAC address {}; consider changing it", hardware_addr);
             }
             #[cfg(soc_platform = "kc705")]
             {
                 hardware_addr = EthernetAddress([0x02, 0x00, 0x00, 0x00, 0x00, 0x01]);
+                warn!("using default MAC address {}; consider changing it", hardware_addr);
             }
-            warn!("using default MAC address {}; consider changing it", hardware_addr);
         }
     }